Earth-Sized Alien Planet Found Around the Stars Next Door

Artist’s impression of a planet discovered orbiting Alpha Centauri B, a member of the triple star system that is the closest to Earth. Our Sun is visible to the upper right. (ESO/L. Calçada)

These days it seems exoplanets are being discovered nearly every week, with “super-Earths”, “hot Jupiters” and “cold Neptunes” being identified (or at least announced as solid candidates) within star systems all around our neck of the galaxy. To top it all off, today the European Southern Observatory announced that an Earth-mass world has now been found orbiting Alpha Centauri B — quite literally the “star next door.”

Using the HARPS (High Accuracy Radial velocity Planetary Search) instrument on the 3.6-meter telescope at ESO’s La Silla Observatory, researchers have identified an Earth-mass planet in orbit around Alpha Centauri B, one of a pair of Sun-like stars in the Alpha Centauri binary system.

Located 4.36 light-years away in the constellation Centaurus, Alpha Centauri A and B (as well as the accompanying smaller, dimmer star Proxima Centauri) are the closest known stars to our solar system. Their combined magnitudes make the Alpha Centauri system the third-brightest star in the night sky.

This newly-discovered world is not only the closest, but also the lightest exoplanet ever discovered around a Sun-like star. Its estimated minimum mass is just slightly more than Earth’s.

Not to have its planet-hunting Kepler, Spitzer and JWST missions outshined, NASA released a statement on October 17 about the HARPS discovery.

“We congratulate the European Southern Observatory team for making this exciting new exoplanet discovery,” said Dr. John Grunsfeld, NASA’s Science Mission Directorate Associate Administrator. “For astronomers, the search for exoplanets helps us understand our place in the universe and determine whether Earth is unique in supporting life or if it is just one member of a large community of habitable worlds. NASA has several current and future missions that will continue in this search.”

Exciting news, yes, but it’s not a complete “eureka” moment just yet: the planet orbits its star much too closely to be within any habitable zone. At only 6 million km (3.7 million miles) from Alpha Centauri B it’s likely a pretty hot place, being about 10 times closer than Mercury is to the Sun. It’s so close, in fact, it’s entire “year” is only 3.2 days long.

Still, these findings demonstrate the highest precision ever achieved using the HARPS method, which measures the minuscule “wobble” of a star caused by an orbiting planet.

“Our observations extended over more than four years using the HARPS instrument and have revealed a tiny, but real, signal from a planet orbiting Alpha Centauri B every 3.2 days,” said lead author Xavier Dumusque of the Geneva Observatory in Switzerland and Centro de Astrofisica da Universidade do Porto, Portugal. “It’s an extraordinary discovery and it has pushed our technique to the limit!”

“This is the first planet with a mass similar to Earth ever found around a star like the Sun. Its orbit is very close to its star and it must be much too hot for life as we know it,but it may well be just one planet in a system of several.”

– Stéphane Udry, Geneva Observatory

The team’s results will appear online in the journal Nature on October 17, 2012.

Voices of Exploration

"I think there’s something to seeing these very professional people helping each other to solve a problem and in the idea that mankind is humane and will do the right thing eventually to each other and to others...we all like the idea that there are great mysteries still to be explored.”
— Leonard Nimoy (1931–2015)

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